Dental Implants. History

Transcription

1 Dental Implants What is a dental implant? A dental implant is called a root form titanium fixture that replaces a natural tooth. It s usually made from titanium, and is a medical device that mimics a missing tooth or a group of teeth. Most dental implants used today are called root-form endosseous implants ; the implants cylindrical appearance is similar to the actual tooth root and is placed within the bone. The jawbone accepts and osseointegrates (becoming part of the bone) with the titanium post. The implant will fuse directly with the jawbone, but it doesn t have the periodontal ligament of a natural tooth. Thus, the implant(s) may feel slightly different than that of a natural tooth. Before the usage of root-form endosseous implants, most implants were either blade endosseous implants (the shape of the metal piece looks like a flat blade) or subperiosteal implants (the metal piece was made to lie directly onto the bone) Dental implants are used to support numerous dental prostheses, such as crowns, implant-support bridges, and dentures. The implants can be used as an anchor for orthodontics. They help to move the teeth more quickly, more effectively. The results are better than if the orthodontics were done without the implants. Dental implants allow unidirectional teeth movement in orthodontists without indirectly moving teeth that are not suppose to move. History The first record of endosseous implants (implants that are embedded in the bone) is during the Mayan civilization, 1,350 years before Per-Ingvar Branemark started working with titanium. During an excavation of Maya burial sites in Honduras in 1934, archaeologists discovered a jawbone fragment from 600 AD, which belonged to a woman in her 20s. She had three tooth-shaped pieces of shell placed where three of her lower incisors were missing. For 40 years, archaeologists thought that these shells were placed post-mortem, as the ancient Egyptians did. However, in 1970, Professor Amadeo Bobbio, a Brazilian dental expert, was studying the jawbone and took a series of radiographs. He noticed there was compact bone formation around two of the implants, which led him to conclude that the implants were placed when the woman was alive, not after she died. During the woman s lifetime, her implants functioned like actual teeth! In the 1950s, researchers at Cambridge University in England were studying blood flow in vivo. They managed to develop a method of making a chamber of titanium, which was then placed into the soft tissue of rabbit ears. In 1952, a Swedish orthopaedic surgeon named Per-Ingvar Branemark was interested in studying bone regeneration and healing. He used the Cambridge designed rabbit ear chamber in the rabbits femurs. Months later, he tried to remove the titanium chambers from the

2 rabbits, but discovered that he couldn t. Branemark noticed that the bone had fused around the titanium, which thus made it impossible to remove. Branemark continued to carry out more experiments by using both animal and human subjects, all of which confirmed this unique property of titanium. Dr. Leonard Linkow placed his first dental implant in By 1992, he had placed over 19,000 dental implants. He wrote 12 books and acquired 36 patents during his career. Meanwhile, Dr. Stefano Melchiade Tramonte, an Italian doctor, knew that titanium can be used for dental restorations. He developed his own titanium screw to support his dental prosthesis and started to use it on his own patients in The results of his clinical studies were published in Even though Branemark originally considered working on the knee and hip, he realized that the mouth was more accessible for continuing clinical experiments and the high rate of edentulism within the general population offered more subjects for widespread study. By 1965, Branemark, who was by then a Professor of Anatomy at Gothenburg University in Sweden, placed his first titanium dental implant into a human subject. Branemark is known as the father of implant dentistry. Research done in the United States led to a 1969 US patent filing for titanium dental implants. Over the next 14 years, Branemark published articles detailing the usage of titanium in dental implants. In 1978, Branemark partnered with the Swedish defense company, Bofors AB, for the development and marketing of his dental implants. Nobelpharma AB was thus created in 1981, focusing on dental implants. Now, over 7 million Branemark System implants have been used and hundreds of other companies are producing dental implants. The majority of dental implants available are shaped like small screws, with either tapered or parallel sides (they can be placed when a tooth is removed and sometimes with the bone beyond the tip of the socket). Implants placed immediately into an extraction socket have similar success rates as those that are placed into healed bone. The success rate and the radiographic results of the immediate restorations of the dental implants that are placed into fresh extraction sockets, with the temporary crowns placed simultaneously, have shown to have similar results to those that are placed later on (the crowns are placed weeks or months later). Some recent research is focusing on using ceramic materials, such as zirconia, in the manufacturing of dental implants. Although Zirconia has the same shape as titanium implants, they have been more successful during orthopaedic surgery. Zirconia also has the advantage of being more cosmetically aesthetic. However, more research needs to be done before one-piece Zirconia implants can be used for daily practice, as results have varied. Composition A normal implant has a titanium screw (which resembles a tooth root) with either a rough or smooth surface. The majority of dental implants are made out of commercially pure titanium, which has 4

3 grades. These grades depend on the amount of carbon and iron. More recently, the usage of grade 5 titanium has increased. Grade 5 titanium is believed to give similar osseointegration levels as commercially pure titanium. Grade 5 titanium offers better tensile strength and fracture resistance. Most implants used nowadays are still made out of commercially pure titanium, but some implants are Grade 5 titanium. The implant s surface may be modified by plasma spraying, anodizing, etching, or even sandblasting in order to increase the surface area, as well as enhancing the osseointegration potential of the implant. Training The ADA does not recognize any sort of specialty for dental implants. Implant surgery can be performed on an outpatient under general anesthesia, oral conscious sedation, nitrous oxide sedation, intravenous sedation or under local anesthesia by trained and certified clinicians that include general dentists, endodontists, oral surgeons, periodontists, and prosthodontists. In the United States, several implant training courses are available through major societies (such as the Academy of Osseointegration, the International Congress for Oral Implantologists, the American Board of Oral implantology, and the American Academy of Implant Dentistry, just to name a few) that focus on providing continuing education after graduation. These courses focus on treatment planning, case selection, implant placement protocol, restorative techniques, and marketing strategies. Surgical Procedure Surgical Planning Prior to surgery, Dr. Singer creates a careful and detailed treatment plan, which is needed in order to identify vital structures, such as the inferior alveolar nerve or the sinus; and the shape and dimensions of the bone in order to properly align the implants for the most favorable outcome. Two-dimensional radiographs, such as orthopantomographs or periapicals, are often taken before the surgery. In many cases, a CT scan is also needed to know where the implants will be placed, as well as to avoid injuring vital nerves. Specialized 3D CAD/CAM computer programs may also be used to enhance the virtual surgery of a CT. A stent may sometimes be used by Dr. Singer to help the placement of the implants. A surgical stent is an acrylic or resin device that fits over the teeth, the bone surface, or the mucosa (where all of the teeth are missing) with pre-drilled holes to show the position and the angle of where the implants are to be placed. After the surgical stent is made, a computerized planning of the case from the CT scan is created. Basic Procedure

4 The placement of an implant requires preparation into the bone by using either hand osteotomes or precision drills with highly regulated speed in order to prevent burning or pressure necrosis of the bone. After a certain amount of time has passed to allow osseointegration to be completed (letting the bone fuse with the implant), a crown, or crowns, can be placed onto the implant. Mini dental implants, on the other hand, can be loaded immediately and still have a high success rate. The amount of time that is needed to replace an implant depends on various factors, such as the experience of the practitioner, the quality and quantity of the bone, and the difficulty of the situation. Detail Procedure At sites where no teeth are present, a pilot hole is drilled into the bone. Drilling to the jawbone usually occurs in several steps. The pilot hole is expanded by using progressively wider drills. Care is taken so as not to damage the bone cells from too much heat. A cooling saline or water spray keeps the temperature of the bone below 47 C. The implant screw can be self-tapping, and is screwed into place at a precise torque to avoid harming the surrounding bone. For most implants, the drilled hole is about 1 mm deeper than the implant in place because of the shape of the drill tip. Surgical Incisions Typically, an incision is made at the site where the implant is to be placed. This is called a flap. Some surgeries perform a flapless surgery, where a piece of the gum tissue is punched-out from over the implant site. Proponents for flapless surgery believe that it decreases recovery time while opponents believe that it increases complications due to the edge of the bone not being visualized. Due to these visualization problems, flapless surgery is often carried out by using a surgical guide such as a computerized 3D planning of a pre-operative CT scan. Healing Time The amount of time required for the implant to osseointegrate varies. Generally, practitioners allow 2-6 months of healing time, but some studies show that early loading of the implant may not increase any early or long term complications. If the implant is loaded too soon however, there is a possibility that the implant may fail. For a failed implant, the amount of time for healing, possible grafting, and placing a new implant may take as long as 18 months. In order to avoid this scenario, many practitioners are reluctant to speed up the healing process. One-stage, Two-stage surgery Once an implant is in place, either a healing abutment or a healing cap is placed on top. When a healing cap is used, it covers the implant as it integrates. A second surgery is thus needed to place the healing abutment. A two-stage surgery is sometimes chosen when a bone graft is done or surgery on the mucosa may be needed for esthetic reasons. Some implants are one piece; thus no healing abutment is needed.

5 In carefully selected cases, a patient can be implanted and restored in a single surgery called Immediate Loading. In these cases, a provisional prosthetic tooth or crown is shaped in order to avoid the force of the bite transferring to the implant as it s integrating with the bone. Surgical Timing There are numerous approaches to place dental implants after tooth extraction. They are: 1. Immediate post-extraction implant placement 2. Delayed immediate post-extraction implant placement (usually 2-3 weeks after extraction) 3. Late implantation (at least 3 months after extraction) Depending on the timing of the loading of the dental implant(s), the procedure for loading can be categorized into: 1. Immediate loading procedure 2. Early loading (1-12 weeks) 3. Delayed loading (over 3 months) Immediate Placement Placing the dental implant right into the extraction site is becoming a more common practice as a way to preserve bone and reduce the treatment time. Furthermore, immediate loading is also becoming a more common practice. By using these two methods, treatment time can be reduced by months. In some cases, the prosthetic tooth can be attached to the implant simultaneously as the dental implant. The success rate of placing a dental implant into a site where the tooth was just extracted is just as successful as placing the implant into a site where the bone has healed. Use of CT Scanning When 3D x-ray imaging (cone beam computed tomography or CBCT) is used before a surgery to accurately pinpoint where the vital structures are, such as the inferior alveolar canal, the mental foramen, and the maxillary sinus are, the risk of complications arising reduces as does chair time and the number of visits. Cone beam CT scanning, compared to traditional CT scanning, uses less than 2% radiation, provides more accuracy, and is safer for patients. CBCT allows the surgeon to create a surgical guide, which thus allows him to accurately angle the implant into the correct space. Complementary Procedures Sinus lifting is a common surgery that is performed during the placement of dental implants. A dentist or a specialist with the proper training thickens the inadequate part of the atrophic maxilla towards the sinus using either bone transplantation or bone expletive substance. More volume is created for a better quality bone site for the implant.

6 Bone grafting will be needed if there is not enough bone to support the implant. Sufficient bone is needed in order for the implant to successfully fuse. Improving the bone s height which is extremely difficult to achieve is particularly important for in order for proper anchorage of the implant s root-like shape because it has to support mechanical stress, such as chewing. Implantologists try to place the implants at least as deeply into the bone as the crown or tooth is above the bone. This is called a 1:1 crown to root ratio. This ratio determines the target of how much bone grafting is needed. If the 1:1 or more can t be achieved, the patient is usually told that a short implant is to be placed instead. Many different types of grafting materials and substances can be used. They can be the patient s own bone, which can be taken from the hip or from a spare jawbone; processed bone from cadavers; cow bone or coral; or even artificial bone. The bone intended to support the implant can be split and widened along with the implant. The bone is then placed between the two halves. This is called a ridge split procedure. Bone grafting surgery has its own protocol for care. The clinician creates a large flap in the gum to fully expose the jawbone at the graft site, performs one or several types of block and onlay grafts in and on the existing bone. Next, the mucosa is carefully sutured over the site. With a cocktail of antibiotics and topical antibacterial mouth rinses, the graft site heals in a span of several months. The clinician then takes a new radiograph to see how the graft site is doing. A 3D or cone beam radiograph can be used to accurately measure the bone and where the nerves and other vital structures are before treatment can go any further. The same radiographic data can be used for computer-designed placement guides. Correctly performed, a bone graft can produce live vascular bone, which is similar to natural jawbone. Therefore, a suitable environment for implants is created. Note: the grafted bone is eventually resorbed by the body and is then replaced by new formed bone. Considerations In order for dental implants to work, there has to be enough bone and it has to be strong enough to support the implant. If there isn t enough bone, a bone graft is needed to ensure the success of the implant. Furthermore, natural teeth and the supporting tissues must also be in good health. For all cases, careful consideration must be given to the final functional aspects of the implant, such as assessing the forces that will be placed on the implant. Implant loading from activities such as chewing, abnormal grinding, or clenching habits, can cause failure due to too much force. The failure can be due to the implant itself, or bone loss (a resorption of the surrounding bone). The dentist has to first decide what type of prosthesis will be used. Afterwards, the type of implant that will be used will be decided. If bone volume or density is not enough, a bone graft must be done first. The dentist might consult with another specialist to co-treat the patient. Usually, models or impressions of the patient s jawbones and teeth are made to be used as physical aids. If one isn t made, an implant

7 surgeon might wish to make one of his own or rely upon advanced computer-assisted tomography or a cone beam CT scan to get the proper treatment plan. Computer simulation software based on CT scan data allows virtual implant surgical placement based on a barium impregnated prototype of the final prosthesis. This allows the dentist to see where the vital anatomy is, the bone quality, implant characteristics, whether there s a need for bone grafting, and maximizing the implant bone surface area. Computer CAD/CAM milled or sterolithography based drill guides can be made for the surgeon to perform proper implant placement based upon the final prosthesis occlusion and aesthetics. A treatment planning software can also be used to demonstrate all of this to the patient on a computer screen. When the surgeon has expressed all possible options to the patient, that same software can be used to produce precision drill guides. Specialized software applications, such as SimPlant or NobleGuide use the digital data from the patient s 3D x-ray to build the treatment plan. A data set is then made and sent to a lab to make the precision in-mouth drilling guide. Success Rates The success rates for dental implants depend on the surgeon/dentist s skills, the quality and quantity of the bone, and the patient s oral hygiene. Implants have a success rate as high as 99% or better. The most important factor that determines if an implant will be successful is the achievement and the maintenance of the implant s stability. Other factors are the patient s overall health and how well he/she follows post-surgical care instructions. Failure The failure of a dental implant is usually related to how well the implant osseointergrates with the bone, or vice-versa. A dental implant is considered to be a failure if it is lost, moves, or shows peri-implant (around the implant) bone less of greater than 1 mm in the first year and great than.2 mm a year later. Dental implants can t get cavities, but they can get peri-implantitis, which is an inflammatory condition of the mucosa and/or bone around the implant. This can cause bone loss and eventual loss of the implant. The condition is usually, but not always, associated with some sort of chronic infection. Periimplantits usually occurs in heavy smokers, patients who are diabetic and patients who have poor oral hygiene. In some cases, the mucosa around the implant is too thin. Currently there is no agreement as to what s the best way to treat peri-implantits. The condition and its causes are not fully understood yet. The risk of an implant failing increases in smokers. Thus, the implant is placed only after a patient has stopping smoking as the treatment can be very expensive. More rarely, an implant can fail due to poor positioning during surgery, or it could be overloaded initially, causing failure to integrate with the bone.

8 If smoking and positioning problems exist before the implant surgery, clinicians may suggest that a bridge or a partial denture is a better solution. Contraindications There are a few absolute contraindications to implant dentistry. However, there are some systemic, behavioral, and anatomic considerations that should be examined. For lower jaw implants, within the vicinity of the mental foramen, there has to be enough alveolar bone above the mandicular canal (the inferior alveolar canal or IAC, which acts as the conduit for the neurovascular bundle carrying the inferior alveolar nerve or IAN). Failure to precisely locate the IAN and MF allows for surgical insult by the drills and the implant too. Such an insult can cause irreparable damage to the nerve, often felt as a general numbness or a painful numbness of the gum, lip, and chin. This condition can continue for life and can be accompanied by unconscious drooling. Uncontrolled Type II diabetes is a major contraindication as healing followed by any type of surgery is delayed due to poor peripheral blood circulation. Therefore, the clinician must consider the volume and the height of the bone that s available. Often an ancillary procedure called a block graft or a sinus augmentation is needed in order to provide enough bone for successful implant placement. Information regarding intravenous and oral bisphosphonates (taken for certain types of breast cancer and osteoporosis, respectively) can put a patient at a higher risk of developing a delayed healing syndrome called osteonecrosis. Therefore, implants are contraindicated for some patients whom take intravenous bisphosphonates. For patients who take an oral bisphosphonate (Actonel, Fosamax, and Boniva to name a few), they may be told to stop taking the medication a few months prior to implant surgery, and then resume several months later. Bruxism (tooth clenching or grinding) should also be considered when creating a treatment plan. The forces during bruxism are very detrimental to implants as the bone is healing; micromovements in the implant s position are associated with an increased rate of the implant failing. Bruxism will continue to pose a threat to the implant(s) throughout the life of the patient. As natural teeth contact a periodontal ligament that allows each tooth to move and absorb shock, implants do not have this capability. The problem can be reduced by wearing a custom made mouthguard at night. After the implants are in place, there are physical contraindications that can prompt rapid action by the implantology team. Excessive or sever pain, or excessive bleeding, that lasts for more than three days is a warning sign. Constant numbness of the gum, lip and chin is another warning sign. In the latter case, which can be accompanied by severe constant pain, it is best to determine if the surgery has insulted the IAN. A 3D cone beam x-ray can provide the necessary data. Before this step is taken, an

9 implantologist might choose to remove the implant instead in an effort to restore never function because delay is usually ineffective. Depending on what is discovered on the 3D x-ray, the patient might be referred to a specialist to repair the nerve. Nonetheless, a speedy diagnosis and treatment is necessary.